- RFT5-dgA is an immunotoxin comprised of the IL-2Ra-specific murine IgG1 antibody RFT5 linked to deglycosylated ricin A chain (dgA) via the sterically hindered heterobifunctional disulfide linker SMPT (4-succinimidyl-oxycarbonyl-a-methyl-a-(2-pyridyldithio)-toluene).